Search Results (306)

The large-scale accumulation of coal gangue has caused serious environmental problems, and converting it into ceramsite is an important pathway for resource utilization. Grinding is a key step in the preparation of coal gangue ceramsite, but the effect of particle size distribution on heat release and ceramsite performance remains unclear. In this study, coal gangue with a calorific value of 699.77 kcal/kg was ground for 1, 2, 3, and 4 h, respectively, followed by pelletizing and sintering. The different ground powders and sintering ceramsites were investigated using particle size analysis, TG-DSC, and XRD, as well as pore structure and strength tests. The results show that for the Datong coal gangue raw material, grinding parameters and sintering regime adopted in this work, the powder milled for 2 h presents a left-shifted particle size distribution curve with a narrow main peak, particle refinement and a concentrated particle size profile (D50 = 8.498 μm, D90 = 23.941 μm). Combined with TG-DSC, XRD, and pore property test results, the 2 h ground powder delivers the most concentrated heat release during low-temperature combustion. This concentrated heat release is inferred to promote high-temperature mineral phase reconstruction and liquid phase formation, thereby generating a dense ceramsite structure featuring low apparent porosity, high closed porosity and excellent mechanical performance (water absorption: 2.99 ± 0.44%; compressive strength: 15.12 ± 0.43 MPa). When the grinding time is extended to 3 h, the particle size distribution broadens, and both the particle size distribution curve and the DSC curve show shoulder peaks, indicating dispersed heat release. Extending grinding time from 3 h to 4 h appears to induce fine-particle agglomeration with heat release becoming more dispersed and decreasing reaction degree, leading to an uneven temperature distribution and deteriorated ceramsite performance. Full article

Circulating fluidized bed (CFB) fly ash exhibits immense potential as a supplementary cementitious material, yet its application is limited by volumetric instability related to delayed ettringite formation. This study investigates the effect of grinding and ultrafine grinding on hydration behavior, microstructure, and long-term volumetric stability of CFB fly ash–cement composites using isothermal calorimetry, XRD, SEM-EDS, TG-DSC, and MIP. Results show that increasing fineness shortens the induction period and advances the second hydration peak by ~6 h. The cumulative heat release of the UCFA system reaches 95.2% of plain cement (85 h). Ultrafine grinding improves hydration activity and reduces total pore volume by 7.32% compared with cement and 22.18% compared with RCFA, leading to denser microstructures and higher compressive strength. Mechanistically, grinding modifies the outer sulfate-bearing layer, accelerating sulfate dissolution and early ettringite formation, while promoting CaO exposure and pozzolanic reactions. Long-term tests up to 730 days confirm that UCFA significantly reduces linear expansion, indicating improved volumetric stability. These results demonstrate that ultrafine grinding simultaneously enhances hydration reactivity and long-term stability, providing a feasible route for high-value utilization of CFB fly ash in cementitious systems. Full article

2.5D C/SiC composites are characterized by high hardness and brittleness. These properties render the composites prone to fiber fracture, burr formation and matrix damage during grinding for hole-making. This study systematically investigates the material removal mechanism, tool wear behavior and machining quality evolution process during diamond core drill grinding for hole-making. Through experiments, the effects of grinding angle and grinding force and the thermal effects on material removal characteristics and hole wall machining quality were analyzed, and the stagewise characteristics of tool wear and the correlation between processing parameters and machining quality were clarified. The results indicate that the wear of diamond core drills undergoes a three-stage evolution: slight abrasive grain shedding at the initial stage, local damage and wear loss at the middle stage, and large-scale abrasive grain peeling followed by tool failure at the late stage. As wear aggravates, the machining axial force increases remarkably and the grinding temperature rises drastically. Hole wall defects gradually develop from minor initial fiber fracture into complex failure modes including burrs, fiber pull-out and matrix damage. In particular, the morphological degradation at the hole exit is the most severe. This study verifies that the optimization of process parameters and tool design can improve machining quality, and provides theoretical guidance and an experimental basis for the efficient and precise machining of high-performance composites. Full article

Anatase-bearing lateritic ores from Qinglong, Guizhou Province, China, are characterized by extremely low TiO₂ grade, high clay content, fine-grained dissemination, and complex intergrowths with iron oxides, which severely hinder efficient beneficiation. In particular, anatase commonly occurs as ultra-fine particles encapsulated by clay minerals or closely associated with iron oxides, and its surface is often covered by nanoscale goethite films, resulting in surface passivation and pseudo-magnetic behavior. These characteristics lead to a pronounced contradiction between mineral liberation and excessive slime generation during conventional grinding processes. To address these challenges, a high-efficiency pre-concentration flowsheet was developed based on selective desliming, stage grinding, intensive scrubbing, flotation, and weak magnetic separation. Selective desliming via hydrocyclones was adopted, which is inferred to preferentially discard true slimes finer than 10 μm while potentially retaining most fine anatase particles within the underflow. Stage grinding was then applied, which may promote the improved liberation of anatase and early rejection of coarse gangue, and may help reduce overgrinding. Intensive scrubbing was introduced, which is expected to weaken or partially remove iron oxide coatings from the anatase surface, thereby potentially restoring surface activity and reducing pseudo-magnetic interference. Subsequent flotation and low-intensity magnetic separation were optimized to increase the concentrate TiO₂ grade and cut iron impurities, which may be associated with improved surface selectivity and weakened pseudo-magnetic responses. Closed-circuit beneficiation tests demonstrated that a TiO₂ concentrate with a grade of 29.62% and a recovery of 65.4% could be obtained from an ore with an initial TiO₂ grade of only 4.39%. Moreover, approximately 40% of the feed mass was rejected at the pre-concentration stage, significantly reducing the load on downstream separation processes. The proposed process demonstrates promising potential as a technical route for the beneficiation of similar refractory anatase-bearing lateritic ores. Full article

Flake graphite is a natural non-metallic material with excellent electrical and thermal conductivity and good lubricity. This study proposed a multi-stage friction–shear cavitating waterjet method to enhance the liberation of flake graphite from gangue minerals. A corresponding nozzle was designed and fabricated by integrating liquid–solid two-phase transport, grinding kinetics, profile-based design, and similarity design. Fluent simulations were conducted with the Eulerian multiphase model to analyze the water–vapor–flake graphite three-phase flow field at different inlet pressures, focusing on vapor volume fraction, water phase flow, and flake graphite particle phase behavior. A distinct cavitation region appeared in the outlet diverging section, mainly near the wall. At inlet pressures of 25 MPa and above, the maximum vapor volume fraction was maintained above 99%, suggesting strong cavitation-inducing capability. Jet liberation experiments showed that the fixed carbon content increased from 49.11% in the feed sample to 78.77% in the waterjet-treated flotation concentrate, while D90 decreased from 121.36 to 103.33 μm and the average particle size decreased from 62.78 to 55.02 μm. These results indicate that multi-stage friction–shear cavitating waterjet treatment facilitates the liberation of flake graphite from gangue minerals, thereby improving the fixed carbon content of the flake graphite concentrate. Full article

Precision glass molding is an economical and resource-efficient method for manufacturing precision optics in a replicative way, offering advantages over conventional manufacturing methods, particularly for complex geometries. However, challenges arise due to different thermal expansion coefficients between the mold and the glass, which lead to shape deviations during the cooling process and require high compensation efforts. This study investigates the machining behavior during ultra-precision grinding of an innovative MAX phase composite whose coefficient of thermal expansion can be specifically adapted to that of glass. The aim is to evaluate the influences of varying process parameters and material configurations on surface integrity and the suitability of ultra-precision grinding for mold manufacturing in the context of precision glass molding. Systematic grinding tests were carried out and complemented by force measurements. The resulting surfaces were characterized using optical measurement technology and atomic force microscopy; in addition, the edge zone was analyzed using transmission electron microscopy. The results confirm the basic suitability of ultra-precision grinding for the MAX phase composite but point to potential subsurface damage that could limit its usability in precision glass molding. Full article

The valorization of drinking water treatment sludge (DWTS) and eggshell waste represents a promising route for reducing landfill disposal and developing alternative stabilized materials for geotechnical applications. This study aimed to evaluate the mechanical and microstructural behavior of DWTS stabilized with commercial lime (CL) and eggshell-derived hydrated lime (EHL), including alkali-activated EHL systems. EHL was produced from locally collected eggshell waste through washing, drying, grinding, calcination at 1000 °C for 4 h, hydration, drying, and sieving. The mixtures were prepared with lime contents of 5%, 8%, 11%, and 14%, while NaOH solutions of 0.5, 1.0, and 1.5 M were used for the activated systems. A total of 120 cylindrical specimens were compacted under controlled dry unit weight and moisture content and cured for 7 and 28 days. The stabilized DWTS was evaluated through unconfined compressive strength (q_u), SEM–EDS analysis, and multifactorial ANOVA. The highest q_u for CL-treated specimens was 4561.72 kPa at 14% lime and 28 days, while EHL reached its best response at 11% lime and 7 days, with a q_u of 3195.13 kPa. In general, EHL showed a competitive performance at intermediate and high lime contents, although increasing NaOH molarity tended to reduce strength. Full article

The problem of chromium contamination, especially Cr(VI), in acidic wastewater has drawn significant attention, requiring effective and sustainable remediation measures. In this study, tannic-acid/Fe₃O₄-modified corn straw biochar (Fe-TA-CSB) is prepared by a grinding-calcination method to remove Cr(VI). The factors influencing the removal effect of Fe-TA-CSB are investigated through static adsorption experiments. The removal mechanism is explored by combining adsorption kinetics, isothermal adsorption, and thermodynamics, as well as characterization methods. The results show that the removal efficiency of Cr(VI) increases with the increase in pH, contact time (t), and solid–liquid ratio (m/v), but decreases with the increase in initial concentration (C₀). Under optimal conditions of TA/Fe₃O₄ mass ratio = 12.5%, pH = 3.0, m/v = 1.0 g/L, and C₀ = 10 mg/L, the removal efficiency value is 94.02%, which is approximately 81.44% after four adsorption–desorption cycles. The adsorption behavior is fitted well by the Sips isotherm model and Elovich kinetics model, suggesting the adsorption process of heterogeneous monolayer chemisorption. The removal mechanism of Cr(VI) by Fe-TA-CSB involves electrostatic interaction with Cr(VI), reduction in Cr(VI) to Cr(III) through C–O and Fe(II), and complexation of reduced Cr(III) with the introduced Fe–O and phenolic hydroxyl groups. Fe-TA-CSB is an environmentally friendly and renewable adsorbent with good potential for the treatment of acidic wastewater. Full article

Edible powders are important food ingredients, and their quality strongly affects processability, stability, and nutrient delivery. Compared with conventional grinding, superfine grinding enables particle-size reduction to the micron or submicron scale and has shown considerable potential for improving the physicochemical and functional properties of food powders. This review summarizes five representative superfine grinding technologies and discusses how different mechanical force fields regulate powder quality through changes in particle size, specific surface area, cell-wall integrity, and macromolecular structure. Current evidence indicates that superfine grinding can improve hydration behavior, dissolution, the release of bioactive compounds, antioxidant activity, and in vitro bioaccessibility, but these effects are highly dependent on raw-material characteristics and processing conditions. At the same time, excessive micronization may induce particle agglomeration, thermal degradation of sensitive components, sensory deterioration, high energy consumption, and potential safety concerns related to ultrafine particles. Therefore, the performance of a single grinding technology is often constrained by intrinsic physicochemical and engineering limitations. Recent studies suggest that combining superfine grinding with pretreatment, interfacial stabilization, or encapsulation strategies can improve powder stability and functionality more effectively than grinding alone. Future research should focus on standardized evaluation systems, mechanistic clarification across food matrices, and integrated process design for industrial application. Full article

Due to their high damping and the associated low dynamic excitation of the machine tool, hydrodynamic guideways are necessary for precision machines such as grinding machines. This article summarizes the development of the measuring system that was integrated into the guiding rail of a linear hydrodynamic bearing and presents the experimental evaluation. The measuring system is aimed at providing a better understanding of the actual transient hydrodynamic pressure and lubrication condition during the reversing sliding motion in the liquid friction range. The system was checked for its frequency response to ensure that the expected pressure rise during the stroke motion can be measured both in relation to the rail width and to the point. The evaluation is based on Reynolds’ analytical hydrodynamic theory, as numerical calculation approaches themselves are also subject to considerable uncertainties, particularly with regard to the actual geometry of the lubrication gap. The novelty of the results lies in the possibility of analyzing the instationary behavior of a reversing linear bearing of a carriage in machine tools at very low pressures as a quasi-2D and 3D pressure curve. Finally, the new possibilities are demonstrated by analyzing the behavior of a carriage with concave sliding surfaces. Full article

A comprehensive and systematic study was conducted to address a series of key technical challenges encountered in the grinding process at a copper mine. These issues included the complex mechanical properties of the feed ore, which led to low grinding efficiency, difficulty in achieving the required grinding fineness for flotation, uneven particle size distribution in the grinding products, and severe occurrences of overgrinding and undergrinding. Based on the semi-theoretical ball diameter formula, the optimal initial ball size distribution for the ball mill was precisely calculated as Φ70:Φ50:Φ40:Φ30 = 15:25:35:25. Through laboratory-scale grinding tests and Discrete Element Method (DEM) simulations, a systematic analysis of multiple indicators under three different ball loading schemes was performed, including the motion state of particles inside the mill, the collision behavior of the grinding media, and the energy distribution. This analysis confirmed the rationality and effectiveness of the literature scheme. Industrial trial results showed the following: the yield of the +0.20 mm fraction decreased by 4.15 percentage points, and the yield of the −0.010 mm fraction and its proportion relative to the −0.074 mm fraction decreased by 10.17 and 19.10 percentage points, respectively. Conversely, the yields of the intermediate separated fraction (−0.20 + 0.010 mm), the easily separated fraction (−0.074 + 0.018 mm) and the −0.074 mm qualified fraction increased by 14.32, 14.13, and 7.29 percentage points, respectively. The grinding technical efficiency improved by 19.55 percentage points. Furthermore, the specific steel ball consumption decreased by 46 g/t, a reduction of 5.07%. The copper concentrate recovery increased by 0.65 percentage points, resulting in an annual increase of 40.51 tons of copper metal, additional revenue of CNY 3.2483 million, and steel ball cost savings of CNY 603,500. Collectively, this optimization generated a total economic benefit of CNY 3.8518 million. By optimizing the ball size distribution, the particle size composition of the grinding products was significantly improved, the flotation indicators were enhanced, and the grinding media consumption cost was reduced, achieving quality improvement and efficiency increase in the mineral processing. This study provides a valuable reference for solving similar grinding problems. Full article

(1) Background: Variations in bean temperature before grinding are a little-studied factor, but they can potentially influence the characteristics of the resulting powder and the chemical and physical properties of the espresso beverage. This study investigated the effect of two heat treatments, heating and cooling, applied to coffee beans immediately before grinding. (2) Methods: The analyses focused on powder particle size distribution (laser diffraction), impact on the operation of the coffee grinder (noise and electrical absorption), chemical-physical properties of the beverage, caffeine and chlorogenic acid content (HPLC-DAD) and profile of volatile organic compounds (HS-SPME-GC-MS). (3) Results: Heating induced a decrease in the content of caffeine and chlorogenic acids and a change in the aromatic profile consistent with phenomena like accelerated aging (increase in hexanal). Cooling treatment had similar, but less pronounced, effects, although it reduced caffeine extraction and some aromatic compounds. (4) Conclusions: The study demonstrated that the temperature of the coffee beans prior to grinding is a key factor to consider in terms of the particle size distribution of the resulting coffee grounds, as well as the content of bioactive compounds and volatile organic compounds, which can significantly influence various aspects of the final espresso’s quality. Full article

The occurrence of short-wave corrugation with wavelengths of 32–44 mm on curved sections of urban express railway lines is particularly pronounced, yet the underlying initiation mechanisms have remained insufficiently understood. Furthermore, conventional mitigation strategies—including the installation of rail dampers and passive grinding—entail substantial maintenance expenditures, thereby hindering their large-scale application. To elucidate the initiation mechanisms of rail corrugation and to formulate effective control measures, the characteristic corrugation parameters under various track structure configurations across an entire alignment were first measured and systematically analyzed. Dynamic interaction models between vehicles and three distinct track typologies were subsequently developed, together with a comprehensive analytical framework for corrugation evolution. The wheel–rail dynamic response characteristics and corrugation growth rates corresponding to each track type were examined, and the wheel–rail coupled vibration modes that exacerbate corrugation propagation in urban express lines were identified. The instantaneous wear behavior of the rail under differing creep regimes was also investigated, leading to the proposal of a novel self-mitigating approach for rail corrugation. The results demonstrate that the excitation frequency of rail corrugation is predominantly confined to the 600–700 Hz range, exhibiting a fixed-frequency characteristic that remains invariant with respect to curve radius, track structure type, and operational speed. An interesting finding is that, although the intrinsic vibration properties of different track structures diverge significantly, the third-order bending resonance of the rail segment situated between bogie wheels is largely unaffected by track-borne vibrations and manifests as a localized wheel–rail resonance within the vehicle–track coupled system. This particular resonance markedly accelerates corrugation development and is identified as the critical governing factor for corrugation initiation in urban express lines, regardless of the underlying track configuration. Furthermore, rail instantaneous wear displays a substantial phase shift under varying creep conditions, with the wear profiles under creep saturation (full sliding) and low creep (rolling–sliding) exhibiting a distinct anti-phase relationship. This insight underpins a novel self-wear suppression strategy: by intentionally mixing rolling–sliding and full-sliding operational regimes, destructive interference between the out-of-phase wear contributions is achieved, resulting in a considerably attenuated corrugation growth rate compared with exclusive rolling–sliding operation. This methodology thus offers a promising and fundamentally new alternative for the long-term management of rail corrugation through intrinsic wheel–rail interaction. Full article

Replacing clinker with mixtures of calcined clay and limestone is one of the most sustainable strategies for decarbonizing the cement industry. However, the kinetic patterns governing the grinding behavior of these materials are not yet fully understood. This study developed a kinetic model based on particle population balance to simulate this process. Experiments were conducted using a standard Bond ball mill, and the samples were characterized by X-ray diffraction. The results show that the grinding of calcined clay and its mixtures with limestone follows first-order kinetics. The proposed model simulates the process with a high degree of accuracy, with residual errors below 1.5% and a coefficient of determination exceeding 99%. Full article

In this study, a brazed diamond micro-powder grinding wheel with Ni-based filler metal was fabricated, which achieved one-step grinding forming of YG-6 cemented carbide rods. The interfacial microstructure, elemental diffusion behavior, and interfacial phases of the brazed diamond micro-powder joint were systematically characterized. Furthermore, the machining performance of the brazed diamond micro-powder grinding wheel was comprehensively evaluated in combination with its service life and the surface roughness of the machined YG-6 cemented carbide rods. The results show that the Ni-based filler exhibits good wettability to diamond micro-powder particles, and the diamonds have a reasonable protrusion height in the filler layer, with no graphitization observed on the surface of the brazed diamonds. During the brazing process, the active element Cr continuously segregates toward the diamond surfaces and reacts progressively with dissolved C atoms on the diamond surfaces, eventually forming a lath-shaped Cr–C compound layer on the diamond surfaces. XRD results identify this compound as Cr₃C₂. Elemental diffusion occurs between the filler layer and the steel substrate, forming a Fe–Ni solid solution diffusion zone. Consequently, the Ni-based filler forms a reliable chemical metallurgical bond with both the diamond micro-powder particles and the steel substrate. The as-prepared brazed diamond micro-powder grinding wheel exhibits excellent service life: a single wheel can grind more than 1300 YG-6 cemented carbide rods on average before failure. The surface roughness (Ra) of the machined YG-6 cemented carbide workpieces remains below 1.6 μm throughout all processing stages, which satisfies the requirements for one-step precision grinding. Full article